Spacerless artificial disc replacements

ABSTRACT

Spacerless artificial disc replacements (ADR) are disclosed. One preferred embodiment includes two saddle-shaped components to facilitate more normal spinal flexion, extension, and lateral bending while limit axial rotation, thereby protecting the facet joints and the annulus fibrosus (AF). Either or both of the superior and inferior components are made of a hard material such as chrome cobalt, titanium, or a ceramic including alumina, zirconia, or calcium phosphate. The articulating surfaces of the ADR are also preferably highly polished to reduce friction between the components. Metals, alloys or other materials with shape-memory characteristics may also prove beneficial.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of U.S. application Ser. No. 14/169,657 (“the '657 Application”), filed Jan. 31, 2014, which is a continuation of U.S. application Ser. No. 13/597,898 (“the '898 Application”), filed Aug. 29, 2012 and now U.S. Pat. No. 8,679,182, which is a continuation of U.S. application Ser. No. 12/789,925 (“the '925 Application”), filed May 28, 2010 and now U.S. Pat. No. 8,277,507, which is a continuation of U.S. application Ser. No. 11/194,786 (“the '786 Application”), filed Aug. 1, 2005 and now abandoned, which is a continuation of U.S. application Ser. No. 10/413,028 (“the '028 Application”), filed Apr. 14, 2003 and now abandoned, each of said applications also claiming the benefit of the filing date of U.S. Provisional Patent Application No. 60/372,520, filed Apr. 12, 2002, the disclosures of all said applications being hereby incorporated herein by reference. The present application and the '657, '898, '925, '786, and '028 Applications also claim the benefit of the filing date of U.S. Provisional Patent Application No. 60/449,642, filed Feb. 24, 2003.

FIELD OF THE INVENTION

This invention relates generally to artificial disc replacements (ADRs) and, more particularly, to devices that operate without softer spacer materials such as polyethylene.

BACKGROUND OF THE INVENTION

Polyethylene spacers are common in some artificial joint situations, including total knee replacements (TKRs). Polyethylene spacers are also used between metal plates in many artificial disc replacement (ADR) designs.

Complications arising from poly debris are well documented, however, including fracture of the spacer once it becomes too thin, absorptions and migration of poly particles throughout the body, and loosening of the bone metal junction as a reaction of the poly debris.

Metal-on-metal and ceramic-on-metal surfaces have much lower wear characteristics. In fact, metal-on-metal surfaces demonstrate 400 times less wear than polyethylene on metal surfaces.

While there have been attempts to limit the use of the poly in ADR designs, all existing approaches constitute call-and-socket configurations which do not inherently limit axial rotation. Instead, axial rotation is limited through the use of multiple ball-and-socket joints or an elongated ball-and-socket joint, which complicates the design.

SUMMARY OF THE INVENTION

The present invention replaces polyethylene artificial disc replacement (ADR) spacers with harder, more wear resistant materials. In the preferred embodiments, an ADR according to the invention includes opposing saddle-shaped components to facilitate more normal spinal flexion, extension, and lateral bending. Preferably, the ADR allows at least 10 degrees of movement on the flexion to extension direction and at least 5 degrees of movement in the lateral bending direction. The saddle-shaped articulating surfaces also limit axial rotation, thereby protecting the facet joints and the annulus fibrosis (AF).

According to the invention, either or both the superior and inferior components are made of a hard material such as chrome cobalt, titanium, or a ceramic including alumina, zirconia, or calcium phosphate. The articulating surfaces of the ADR are also preferably highly polished to reduce friction between the components. Metals, alloys or other materials with shape-memory characteristics may also prove beneficial.

The vertebral surfaces of the components may be treated to promote bone ingrowth. For example, the vertebral surfaces of the components may have plasma spray or beads. Alternatively, one or both components may be cemented to the vertebrae. The vertebra-facing surfaces may also include projections such as keels that fit into the vertebrae. In embodiments adapted for cementation, one of the components could be made of polyethylene or other softer material.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is an anterior view of an ADR according to the invention;

FIG. 1B is a lateral view of the ADR of FIG. 1;

FIG. 1C is an oblique view of the ADR of FIG. 1;

FIG. 2A is a view of the anterior aspect of an alternative embodiment of the ADR;

FIG. 2B is a view of the lateral aspect of an alternative embodiment of the ADR shown in FIG. 2B;

FIG. 3A is a view of the anterior aspect of an alternative, less constrained, embodiment of the saddle-shaped ADR shown in a fully flexed position;

FIG. 3B is a view of the lateral aspect of the embodiment of the ADR shown in FIG. 3A;

FIG. 4A is a view of the lateral aspect of another embodiment of a saddle-shaped ADR;

FIG. 4B is a view of the anterior aspect of the embodiment of the ADR shown in FIG. 4A in a fully flexed position;

FIG. 4C is a view of the anterior aspect of an alternative embodiment;

FIG. 4D is a view of the anterior aspect of the ADR shown in FIG. 4A; and

FIG. 4E is a view of the anterior aspect of the ADR shown in FIG. 4A.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1A is an anterior view of an ADR according to the invention. FIG. 1B is a lateral view of the ADR of FIG. 1. FIG. 1C is an oblique view of the ADR of FIG. 1.

FIG. 2A is a view of the anterior aspect of an alternative embodiment of the ADR, wherein the articulating surfaces of both components have a flat area centrally from the front to the back of the ADR. FIG. 2B is a view of the lateral aspect of an alternative embodiment of the ADR drawn in FIG. 2B. The flat area of the articulating surfaces courses centrally from side of the DR to the other side. The flat area allows one component to translate slightly on the other component. Alternatively, a curved area with a large radius could replace the flat area.

FIG. 3A is a view of the anterior aspect of an alternative, less constrained, embodiment of the saddle-shaped ADR drawn in a fully flexed position. The less constrained embodiment facilitates spinal flexion, extension, and lateral bending. FIG. 3B is a view of the lateral aspect of the embodiment of the ADR drawn in FIG. 3A.

FIG. 4A is a view of the lateral aspect of another embodiment of a saddle-shaped ADR. The center of rotation for flexion and extension is not necessarily located in the center of the ADR. For example, the center of rotation is preferably located in the posterior half of the ADR. FIG. 4B is a view of the anterior aspect of the embodiment of the ADR drawn in FIG. 4A, drawn in a fully flexed position.

FIG. 4C is a view of the anterior aspect of an alternative embodiment, showing how the radius of curvature of the articulation for lateral bending may be different than the radius of curvature for articulation for flexion and extension. For example, the radius of curvature for the articulation for flexion and extension, as seen in FIG. 4A, may be smaller than the radius of curvature for the articulation for lateral bending, as seen in FIG. 4C. Articulating surfaces with smaller radii, facilitate movement. Thus, the embodiment of the ADR drawn in FIG. 4A flexes and extends more easily than the embodiment of the ADR drawn in FIG. 3A. The ADR is drawn in a fully flexed position.

FIG. 4D is a view of the anterior aspect of the ADR drawn in FIG. 4A. The ADR is drawn in a neutral position. The area of the drawing with diagonal lines represents the articulating surface of the lower ADR component. FIG. 4E is a view of the anterior aspect of the ADR drawn in FIG. 4A, also drawn in a fully extend position. 

1. A method of implanting an artificial disc replacement comprising: providing an artificial disc replacement comprising: a first component having a first articulating surface and a first vertebral contact surface for engaging a first vertebral body, the first articulating surface including first and second lateral edges and a toroidal region extending between the first lateral edge and the second lateral edge; and a second component having a second articulating surface opposed to the first articulating surface and a second vertebral contact surface for engaging a second vertebral body, the second articulating surface including third and fourth lateral edges and a toroidal region extending between the third lateral edge and the fourth lateral edge; engaging the first and second vertebral contact surfaces of the first and second components with first and second adjacent vertebral bodies of a spinal canal; and articulating the first component relative to the second component so that the first and second articulating surfaces engage with one another to allow for movement of the first vertebral body relative to the second, adjacent vertebral body.
 2. A method of implanting an artificial disc replacement according to claim 1, further comprising limiting axial rotation of the first component relative to the second component to a predefined range.
 3. A method of implanting an artificial disc replacement according to claim 1, wherein the first articulating surface is defined by a concave arc having a radius of curvature A about a first axis, and a convex arc having a radius of curvature B about a second axis perpendicular to the first axis, and the second articulating surface is defined by a convex arc having a radius of curvature C about a third axis, and a concave arc having a radius of curvature D about a fourth axis perpendicular to the third axis, the radius of curvature A, D of at least one of the concave arcs being different than the radius of curvature B, C of at least one of the convex arcs.
 4. A method of implanting an artificial disc replacement according to claim 3, wherein the first and second articulating surfaces are saddle shaped.
 5. A method of implanting an artificial disc replacement according to claim 1, wherein the toroidal regions of the first and second articulating surfaces, respectively, are defined by continuous curves.
 6. A method of implanting an artificial disc replacement according to claim 1, further comprising engaging projections extending from the first and second components with the first and second vertebral bodies, respectively.
 7. A method of implanting an artificial disc replacement according to claim 6, wherein the projections are selected from the group consisting of flanges and keels.
 8. A method of implanting an artificial disc replacement according to claim 1, wherein the first articulating surface includes a single substantially continuous concave surface and a single substantially continuous convex surface, and the second articulating surface includes a single substantially continuous concave surface and a single substantially continuous convex surface.
 9. A method of implanting an artificial disc replacement according to claim 3, wherein the radius of curvature A, D of at least one of the concave arcs is greater than the radius of curvature B, C of at least one of the convex arcs.
 10. A method of implanting an artificial disc replacement according to claim 1, wherein the first and second components are configured to facilitate flexion, extension, and lateral bending of the first and second vertebral bodies while limiting axial rotation.
 11. An artificial disc replacement (ADR), comprising: an inferior component; a superior component; and a smooth, continuous interface between the inferior component and superior components, the interface including at least one convex surface articulating with a corresponding concave surface.
 12. The ADR of claim 11, wherein both components are metallic or ceramic.
 13. The ADR of claim 11, wherein the components are physically configured to facilitate flexion, extension, and lateral bending while limiting axial rotation.
 14. The ADR of claim 11, wherein the components are saddle-shaped.
 15. The ADR of claim 11, wherein the vertebral surfaces of one or both of the components are treated to promote bone growth.
 16. The ADR of claim 11, wherein one or both of the components are cemented to a respective vertebral endplate.
 17. The ADR of claim 11, wherein one or both of the components include projections adapted to fit into a respective vertebral endplate.
 18. The ADR of claim 11, wherein one of the components is made of polyethylene. 